1. Field of the Invention
The present invention relates to a developing device for use in a picture forming apparatus such as an electrophotographic copier, a laser printer and the like and more particularly to a developing device of the type having a devloping tank and a supply tank and which is provided with a sealing member for closing a toner supply outlet of the supply tank before use.
2. Description of the Prior Art
An example of conventional developing device is shown in FIG. 1. The conventional developing device is of the type in which when shortage of toner takes place, the whole of the developing device is exchanged as a unit in order to make the user free from troublesome toner exchange. The developing device is for two-component development and it has a unitary structure comprised of a developing tank 1 disposed near a photoreceptor of the copier and the like and a supply tank 2 for supplying toner T to the developing tank 1, wherein a supply roller 4 is arranged at a toner supply outlet 3 of the supply tank 2 and when the concentration of toner inside the developing tank 1 is decreased, the supply roller 4 is rotated to feed the toner T to the developing tank 1.
In FIG. 1, reference numeral 5 designates a stirrer member for stirring the toner T inside the supply tank 2 so as to convey toner T toward the toner supply outlet 3, 6 a developer roller and 7 a stirrer roller.
In the aforementioned developing device, the surface of the supply roller 4 is in general foamy and therefore, when vibrations are applied to the developing device during its transportation before use, the toner T sometimes spills into the developing tank 1 through a gap formed in the supply outlet 3. As a result, the composition ratio of toner T inside the developing tank 1 exceeds an initially set reference to degrade the picture quality as compared to that initially obtained.
In connection with the above problem, a technique for preventing the spill-out of toner through the toner supply outlet of the supply tank before use has been disclosed (See Japanese Patent Laid-open No. Sho 63-9237). In this literature, as shown in FIG. 2, a sealing member 8 which can be pulled out externally during use is arranged at a toner supply outlet 3 of a supply tank 2 to close a supply tank 2.
In the prior art developing device shown in FIG. 2, however, since the sealing member 8 is pulled out externally, toner T carried on the sealing member 8 tends to be also drawn to the outside to soil the surroundings.
In addition, the user is forced to undertake the troublesome pull-out operating of the sealing member before use.
A developing device for solving the problems described so far is disclosed in U.S. Pat. No. 4,998,140. In the prior art developing device, when the main body of the developing device is attached to the copier main structure, a driving means of a take-up shaft for winding up a sealing member and a driving means of the copier main structure are connected to each other by means of a connecting means. When the power supply of the copier main structure is turned on under this condition, the take-up shaft is rotated while winding up the sealing member to remove it from the supply outlet of the supply tank.
This prior art developing device however needs the take-up shaft, driving means and connecting means which are dedicated to wind-up of the sealing member, raising a problem that the number of parts is increased to make the construction complicated.